Is there ever a point where all the valves are closed?

[Elkins45]

For the sake of simplicity let’s consider a four cylinder gas engine, but in specific I’m asking about a Subaru boxer engine. Is there ever a point in the cycle of a four cylinder engine where all intake and exhaust valves are closed? My gut feel says no because if you park it with the pistons at opposite ends then the exhaust would be open on the one at the end of the exhaust stroke and the intake open on the intake stroke. If you stop it with all four in the middle then the same situation applies because only the pistons on the power and compression strokes will be closed.

The thought behind the question was prompted by the difficulties of doing a piston soak on a V and especially an H engine. It occurred to me that if you were really committed to doing it you could just drain the oil, install the plug and then pour it full of solvent until you reached the top edges of the pistons, but that wouldn’t work because the solvent would just pour out the open set of valves. There’s the additional issue of the air trapped under the pistons in a V, but that could potential be alleviated by taking the plugs out and filling that space from the top…but of course the open valves mean you would have the same problem. And yes, I do know I initially said four cylinder and there aren’t many V4 engines out there.

Parking all the pistons halfway down in a V means they might get wet before the level reached the valves, but that wouldn’t work on an H, and I assume on a V6 or V8 the two banks are staggered so that they are never all at mid level at once? Maybe just keep adding as the level drops, since theoretically the rings would only allow the solvent to leak by very slowly?

Just thinking about stuff…

 

[CarlB]

Is there ever a point where all the valves are closed?​

Yes, but a closed valve still has some leakage. (tiny amount if things are kosher)

 

[skyactiv]

Nope. The answer why involves more typing than I'm willing to do.

 

[eljefino]

Single cylinder, yes. Anything more, no. Look at cam lobe durations in degrees.

I've done a few 4 cylinders timing chains/ belts and the cam will want to rest at a point where all the valves are somewhat open, as the valve spring pressures equalize. Rotate from that point and some will be yet more open while others may close.

There are doodads that adapt shop air to spark plug threads. You could use these to test which cylinders are "closed" and therefore ready for piston soaks. Log the ones you've done, clear the cylinders to avoid hydro locking, then rotate the crank and do some more until they're all done. It's similar to valve adjustment-- if they were all closed, you could do them all at one time without rotating.

 

[TCL]

There is a point when they are all open....when you float the valves.

 

[Elkins45]

Single cylinder, yes. Anything more, no. Look at cam lobe durations in degrees.

I've done a few 4 cylinders timing chains/ belts and the cam will want to rest at a point where all the valves are somewhat open, as the valve spring pressures equalize. Rotate from that point and some will be yet more open while others may close.

There are doodads that adapt shop air to spark plug threads. You could use these to test which cylinders are "closed" and therefore ready for piston soaks. Log the ones you've done, clear the cylinders to avoid hydro locking, then rotate the crank and do some more until they're all done. It's similar to valve adjustment-- if they were all closed, you could do them all at one time without rotating.

In this particular case of a boxer engine I’m thinking about introducing the solvent from the bottom of the piston instead of the top so you couldn’t control which cylinders get the liquid. The more I think about it the more I think it wouldn’t be a big deal because the migration speed of the solvent past the rings would be slow enough you woukd get a good soaking before you lost much of the solvent.

It would probably be smart to pull the manifolds away so any leakage could be kept from pooling in places where it shouldn’t be, but that’s a lot of effort too. Of course this is all just thinking aloud. I don’t even own a Subaru.

 

[dishdude]

They're all closed in a single cylinder during the compression stroke of that individual cylinder.

 

[SubieRubyRoo]

It’s likely almost physically impossible to fill a Boxer this way. The only way I could think of would be to get all the exhaust valves closed (pull the rocker arms?), and put a radiator-style purging funnel into the oil fill tube. I wouldn’t give one RA if the solvent got past the piston in enough quantity to reach the intake manifold… it would clean the intake port.

Just do the logical thing and run HPL, HPL EC, or VRP to achieve the same results with zero risk and zero extra work to achieve the likely minimal result.

 

[Elkins45]

It’s likely almost physically impossible to fill a Boxer this way. The only way I could think of would be to get all the exhaust valves closed (pull the rocker arms?), and put a radiator-style purging funnel into the oil fill tube. I wouldn’t give one RA if the solvent got past the piston in enough quantity to reach the intake manifold… it would clean the intake port.

Just do the logical thing and run HPL, HPL EC, or VRP to achieve the same results with zero risk and zero extra work to achieve the likely minimal result.

That's exactly what I was thinking about. Get a few gallons of toluene/acetone/MEK and fill 'er up to the brim. You could catch most of it when you drain the crankcase and reuse it.

Like I said, I don't even own a Subaru. I'm just amusing myself with "what if?" questions.

 

[JohnnyJohnson]

I guess the best analogy might be is there many moment all 8 Partying women's mouths might be closed?

 

[PandaBear]

Can it be done? Probably, but it may not seal completely long enough for any chemical soak to work long enough. It would leak down the ring over time where it is not stuck and never clean out enough on the part that is stuck. If you want to close all valves you also have to fight the air that's already inside.

I would just run HPL or something like that, or a thicker high detergent oil and change frequently. If it is too bad maybe swap the engine out for a re-ring.